This invention relates to methods and compositions for the control of coccidial infections in animals. In particular, the invention relates to the use of yeast cell and yeast cell wall-containing preparations for use in control of coccidial infections in mammalian and avian species.
Coccidiosis is a protozoan parasitic infection of mammals and birds caused by species of the coccidia Eimeria resulting in intestinal lesions, diarrhea, enteritis and death. Eimeria spp. (E. tenella, E. maxima, and E. acervulina) are three of the most common coccidia that plague the poultry industry. These species differ in their mode of action. E. tenella attacks the cecum, whereas E. maxima and E. acervulina attack the mid and upper regions of the intestinal tract, respectively.
Coccidiosis is an economically important disease in domestic livestock production and even in less severe infections, losses in feed conversion efficiency and decreased weight gains may represent the difference between profit and loss in modem, intensive animal production situations. Coccidial infections are known to be a predisposing factor to other syndromes, in particular, necrotic enteritis (a bacterial infection of the intestinal lining resulting in necrosis of the intestinal lining in various regions of the gut).
Coccidial organisms survive in the environment because of their exceptional reproductive ability and because of the composition of the walls of their oocysts, which provides extraordinary survival abilities for significant periods of time. Oocysts are disseminated via the feces and litter but may also be disseminated in an airborne fashion, such as by movement of dust, and by vector organisms such as earthworms, beetles, flies, and other pests. Because it is standard practice in the poultry industry, for example, to reuse litter, coccidia in litter from previous infected flocks serves as a reservoir for future infections.
Conventional disinfectants are relatively ineffective against coccidia. Thorough cleaning of housing and strict bio-security measures are necessary to maintain proper hygiene and reduce the number of oocysts to which animals and birds are exposed. Unfortunately, due to relatively rapid turnaround of potential host animals (for example, the rapid replacement of flocks in broiler operations), a permanent reservoir of oocysts is often maintained. Even a few oocysts are capable of initiating a massive infection in a few weeks. Accordingly, control measures that go beyond maintenance of proper hygiene are required.
Currently known methods of coccidial control include use of anticoccidial medication and vaccination protocols. Anticoccidial drugs are generally effective for their intended purpose; they advantageously are provided in the feed or via the drinking water to animals being treated. Exemplary drugs include ionophores (Monensin, lasalocid) and chemical anticoccidials. A significant disadvantage of current drugs used for treatment/control of coccidia is that, over time, treated organisms may become resistant to particular drugs. Accordingly, different drugs must be used, often in rotation or in a staggered schedule (shuttle programs), to prevent development of resistant organisms. Even in cases where shuttle programs are implemented, it is possible that efficacy against coccidial infections will be compromised during the period when anticoccidial drugs are altered. Additionally, certain drugs, while useful in the control of coccidiosis, require a predetermined withdrawal period prior to slaughter or consumption of animal products to address safety issues associated with the sale of meat, milk and eggs from treated animals.
Currently employed vaccines against coccidial organisms are also generally effective for their intended purpose, creating an active immunity against infection in treated animals. Vaccines are costly and suffer from the disadvantage that they must contain the appropriate antigens to stimulate a protective immune response to each species of coccidial organism involved in disease processes. In poultry, for example, this could be any or all of the seven species of the genus Eimeria that infect chickens. Further, vaccination protocols may cause subclinical infections of varying severity, and thus, negatively affect performance in those vaccinated animals.
Accordingly, there remains a need in the art for alternative methods for controlling coccidial infections in livestock, with the benefit of improved productivity and economics and where those alternate methods do not lead to the development of resistant organisms and/or require long withdrawal periods prior to slaughter.